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T Y P E 1398-A PULSE GENERATOR
F i g u r e
3-1.
T y p i c a l sensitivity-vs-frequency characteristics.
3.3.2
EXTERNAL DRIVE PROCEDURE.
For external operation, s e t the P R F switch to
EXT DRIVE and apply the external driving signal t o
the EXT DRIVE binding posts. The AF control now be-
comes a triggering level adjustment; the input circuits
are s e t for maximum sensitivity when t h i s control i s
centered.
The input circuit i s dc-coupled, and the pulse
generator will operate from pulses a t any low frequency
desired. The input signal must therefore either be a t a
dc potential c l o s e to ground or be ac-coupled, with an
external blocking capacitor.
3.3.3 OPERATION WITH OSCILLOSCOPE.
trigger, adjust the AF control until triggering i s re-
established. When no further adjustment of the
AF
control will re-establish triggering, the triggering
threshold h a s been reached ( t h i s should be a t about
0.3 volt, p-to-p, t o 1 kc/s ). A plot of typical s e n s i -
tivity is given in Figure 3.1.
g. R e s e t the generator amplitude t o 1 volt, rms. If
possible, display i t s output waveform and the Type
1398-A output pulse simultaneously on the oscillo-
scope.
h. Adjust the
AF
control and observe the starting
point of the pulse. Note that the
AF
control adjusts
the p h a s e at which the pulse i s formed, and that the
pulse always starts during the negative-going input
T o observe external operation on an oscilloscope
transition.
proceed a s follows:
a. Set up the equipment to display a 1-kc square
wave, a s described in paragraph 3.2.4, a t o 1.
b. Set the P R F switch t o EXT DRIVE.
c. Connect an adjustable audio-frequency generator
to the EXT DRIVE binding posts and s e t the gener-
ator to produce a 1-kc s i g n a l of a t l e a s t 1 volt, rms.
d. Center the AF control (now used a s a triggering
level control). The oscilloscope should display a
square wave a s described in paragraph 3.2.4.
e . Decrease the frequency of the audio-frequency
generator. Note that the external generator controls
the prf of the Type 1398-A.
f. Reset the audio-frequency generator to
1
kc/s and
reduce i t s amplitude. When the Type 1398-A fails to
TABLE 3
-
1
DURATION ACCURACY VS DUTY RATIO
Duty Ratio
Accuracy
0 to 20%
f2%
of full s c a l e with
with DURATION dial at 1 to 4.
k5% of reading
with DURATION dial
at
5 to 10.
1 3 5 n s with durations of
0.1 t o 0 . 7 ~ ~ .
20 t o 50%
+ l o % of reading.
I
Over 50%
Inaccurate.
I
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